Apparatus for removing sludge

ABSTRACT

Sludge returned to a tank containing a metal pretreating solution, for example zinc phosphate, is continuously removed from the bottom of the tank by a pump at a rate which is in excess of the capacity of a clarifier device to effect separation of sludge from solution and is delivered to a centrifugal cleaner in which the sludge is concentrated to a flow rate within the capacity of the clarifier device to which the concentrate is delivered from the cleaner.

United States Patent Windall [451 Mar. 12, 1974 APPARATUS FOR REMOVINGSLUDGE [75] Inventor: Roy Sidney Windall, Seal, England PrimaryExaminerwuoyd King [73] Assignee: Carrier Engineering Company I Limited,London, England 22 Filed: May 2, 1972 1 ABSTRACT Appl. No.: 249,704

[30] Foreign Application Priority Data May 12, l97l Great Britain14,495/71 52 US. Cl. 239/124 [51] Int. Cl B05b 9/00 [58] Field of Search239/124 5 6] References 'Cited I UNITED STATES PATENTS 2,763,575 9/l956Bede 239/124 X Sludge returned to a tank containing a metal pretreatingsolution, for example zinc phosphate, is continuously removed from thebottom of the tank by a pump at a rate which is in excess of thecapacity of a clarifier device to effect separation of sludge fromsolution and is delivered to a centrifugal cleaner in which the sludgeis concentrated to a flow rate within the capacity of the clarifierdevice to which the concentrate is delivered from the cleaner.

7 Claims, 5 Drawing [Figures cat/96372 PATENIEDMAR 12 I974 sum 1 0F 3BACKGROUND OF THE INVENTION 1. Field of the invention This inventionrelates to a method of removing sludge or other solid matter formed insolutions used in metal pre-treatment processes.

2. Description of the Prior Art As is well understood metal which is tobe painted or otherwise finish-coated is first subjected to one or morepre-treatment processes, to prepare the surfaces thereof to receive thepaint or other finish-coating. One example of such pre-treatment is thatapplied to automobile bodies which, before, and usually as part of acontinuous process, are subjected to spraying with or dipping intosolutions for cleaning or surface treating the metal while being movedin succession through spray booths appropriate to the kind of cleansingor treatment at each cleansing or treatment stage. One of these stagesis a zincor an iron-phosphating process which results in the productionof sludge which is returned to a tank in which insoluble salts formedduring the phosphating process settle to form sludge which must beremoved from the tank, the solution from which the salts have settledbeing pumped again to the spray nozzles.

Heretofore one or other of three methods have usually been used toremove sludge from the tank, these methods being known as manualde-sludging, continuous de-sludging by vacuum or pressure-assistedfilters, and continuous de-sludging using sludgesettling cones toconcentrate the sludge.

Manual de-sludging is generally only used in connection with plant forpre-treating small metal objects and consists of an operative enteringthe tank and manually digging out the sludge. This method entailsstopping the treating process, is messy, is time consuming, and does notgive a constant solution strength. When using this method solution isperiodically pumped out of the phosphate tank into another tank beforethe operative enters the phosphate tank to dig out the sludge. Theinterval between cleanings of the phosphate tank may be from one to fourweeks depending on the throughput of objects to be treated and for aplant having a very high rate of production even one week betweencleaning operations may be too long. Because it is necessary to stop theplant during cleaning of the tank this operation is usually carried outduring a week-end and for week-end working labour costs are high.

Continuous de-sludging by vacuum or pressureassisted filters is aprocess which is satisfactory and this process entails pumping sludge ata low concentration from settling cones located under the phosphate tankand using vacuum or pressure-assisted filters to deal with the largevolumes of liquid involved. In connection with large phosphate tankssequencing controls may be used so that sludge is removed from each ofthe settling cones in rotation. This process is seldom used because theequipment necessary to carry it into effect is very expensive.

Continuous de-sludging using sludge-settling cones to concentrate thesludge is the method hitherto most commonly used and this method entailspumping sludge continuously from settling cones beneath the phosphatetank and over a clarifier which is a band filter made of filter paperwhich is drawn from a reel across a clean liquid collector and over aroller. Solution and sludge is pumped from the cones at a rate which isabout equal to the capacity of the filter to effect filtering of thesludge from solution and the filtered solution drains through the filterpaper into the collector from which it is returned to the phosphate tankand the sludge collects as a cake on the filter paper. The capacity ofthe filter is about 12 to 25 gallons per minute according to the size ofthe filter. The filter paper lies on the band filter in the form of a.trough and when the thickness of the sludge on the paper is too great toallow liquid to run through the filter as fast as it is being suppliedto the filter, the liquid level in the trough rises and operates a floatswitch which causes the band filter to run on and expose a fresh sectionof filter paper. The filter paper carrying collected sludge is collectedin skips for removal and disposal thereof. Although this method has beenthat which hitherto has been the most commonly used it has the followingdisadvantages:

I. As the capacity of the band filter is restricted to about 20 gallonsper minute the volume of flow of liquid and sludge from each settlingcone is low and this leads to frequent blockages in the settling conesand the pipes from the cones to the filter. The use of pipes of smallerdiameter in an effort to increase the velocity of liquid and sludgetherethrough only leads to a greater tendency for the pipes to becomeblocked due to the restriction of the passages.

2.- The only practical way of checking to detect blockages is for anoperator to check the warmth of the sludge pipes beneath the settlingcones. The phosphate solution is used hot, at a temperature of about Cso that by placing a hand on a sludge pipe just below the settling coneone can tell if the cone is blocked because if it is blocked the pipewill be cold. It is found that operators are usually unwilling to makethe frequent checks necessary, such checks usually requiring to be madeat least once an hour.

3. When a blockage is detected it is removed by passing compressed airinto the pipes. This action cannot usually be carried out duringproduction hours because the admission of the compressed :air violentlydisturbs the sludge in the tank thus causing much of the sludge to enterthe spray circuit where it may become deposited in heat exchanger tubes,block spray nozzles, and collect on an object being sprayed.

The present invention is concerned with improving the last describedmethod and it is a main object of the invention so to improve thatmethod as to reduce to a minimum the above-mentioned disadvantagesthereof.

SUMMARY According to one aspect of the invention there is provided in aprocess for pre-treating metal objects, for example a zinc-phosphatingprocess, in which a treating solution is pumped from a tank to spraynozzles by which the solution is applied to the objects and is returnedto the tank, and a mixture of sludge and solution is removedcontinuously from the bottom of the tank and is delivered to a clarifierdevice by which the sludge is separated from solution, the method ofremoving sludge which includes the steps of continuously transmittingsludge and solution from the tank at a rate in excess of that of thecapacity of the clarifier device to effect separation of sludge fromsolution, and at a position between the tank and the clarifier deviceeffecting concentration of the sludge to a flow rate thereof within thecapacity of the clarifier device.

According to another aspect of the invention there is provided apparatusfor pre-treating metal objects with a treating solution, for examplewith zinc-phosphate, comprising a tank to contain the solution, spraynozzles arranged to apply solution to the objects, a solutionpumpoperable to pump solution from the tank to the spray nozzles throughsolution-delivery pipes connecting the solution pump to the nozzles, aclarifier device operable to separate sludge from solution, asludgedelivery pipe through which sludge and solution can pass from thebottom of the tank to the clarifier device, and a sludge-pump operablecontinuously to transmit sludge and solution from the bottom of the tankthrough the sludge-delivery pipe to the clarifier device, wherein asludge-concentrating device connected to the sludge-delivery pipe isoperable to concentrate sludge to a flow rate thereof within thecapacity of the clarifier device and the sludge-pump is operable totransmit sludge and solution to the sludgeconcentrating device at a ratein excess of that of the capacity of the clarifier device to effectseparation of sludge from solution.

BRlEF DESCRIPTION OF THE DRAWlNGS FIG. l is a diagrammatic elevation ofapparatus for carrying out the method according to the invention,

FIG. 2 is a diagrammatic elevation of a sludgeconcentrating deviceembodied in the apparatus of FIG. ll,

FIG. 3 diagrammatically illustrates the mode of operation of the deviceof FIG. 2, and

FIGS. 4 and 5 are diagrammatic elevations of modified forms of theapparatus shown in F110. ll.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, metalobjects 1 are, in known manner, moved in succession by a conveyor 2through a pre-treatment compartment 3, which for the purpose ofexplanation is assumed to be a booth in which automobile bodies aresubjected to a zinc phosphating process prior to painting. The zincphosphate solution is contained in a tank 4, and a solution-pump 5 pumpsthe solution through a heater 6 and solution-delivery pipes 36 to spraymeans 7 which sprays the solution on to the bodies. The solution drainsfrom the bodies and is returned to the tank, together with sludge, by apipe 8. Sludge-containing solution which settles in the tank 4 iswithdrawn therefrom by a suction sludge-pump 9 which is connecteddirectly to the bottom of the tank 4 through pump-isolating valves 10and a collector pipe 11. Solution substantially freed from sludge as theresult of settling of the sludge passes over a weir 12 into the portion113 of the tank to which the pump 5 is connected.

The pump 9 feeds sludge-containing solution from the tank to at leastone sludge-concentrating device shown as a centrifugal cleaner 14 whichis arranged to concentrate the sludge and to deliver the concentratedsludge through an outlet 15 from the cleaner 14 to a clarifier 16. Theclarifier, which is of known construction, comprises a band 1'7 offilter paper which is drawn from reel 18 across a clean liquid containeror trough 19 from which filtered liquid (solution) is returned bygravity through a pipe 20 to the tank 4. When the thickness of sludge onthe band 117 is too great to allow liquid to run through the filter asfast as it is being supplied to the filter the liquid level in thetrough rises and, in known manner, operates a float switch, not shown,which causes the band 17 to run on and expose a fresh section of theband. The band 17 carrying collected sludge moves downwards through achute 21 and is collected in a skip 22 by which it is removed fordisposal.

The outlet 15 may be an opening the size of which is predetermined tocontrol the rate of delivery of sludge from the cleaner 14 according tothe capacity of the band 17 to deal with the sludge delivered thereto orit may comprise an adjustable valve which can be adjusted to control therate of delivery of sludge to the band 17. The outlet 15 is adjusted bythe valve or by the use of alternative orifices of predetermined size sothat the rate of delivery of sludge from the cleaner 14 is compatiblewith the capacity of the clarifier 16 to deal with the sludge deliveredthereto. It will be understood that the size of the outlet 15 will alsobe set according to the anticipated quantity of sludge contained in thesolution delivered to the cleaner l4 and will depend, among otherthings, on the quantity or concentration of sludge being fed to thecleaner, that is if the sludge is highly concentrated the outlet 15 willneed to be larger because otherwise the cleaner may tend to becomeblocked, on the other hand if the sludge concentration is light asmaller outlet size can be used.

The mixture of sludge and solution is pumped continuously from the tank4 and is delivered to the centrifugal cleaner 14 through asludge-delivery pipe 23 at a rate which is in excess of that of thecapacity of the band 17 to effect separation of sludge from solution.The sludge-containing solution enters the cleaner 14 at a position 24near the top thereof and solution having a lower sludge concentrationthan the solution which entered the cleaner at position 24 leaves thecleaner at 25 from the top of the cleaner and is returned by asolution-return pipe 26 to a return header 27 in the tank 4. In oneembodiment of the invention sludge-containing solution is pumped to thecleaner 14 at the rate of about 1 10 gallons per minute, concentratedsludgecontaining solution is delivered to the clarifier at the rate ofabout 10 gallons per minute, and solution is returned from the cleanerto the tank 4 at the rate of about gallons per minute.

In the event that one centrifugal cleaner and clarifier is notsufficient to deal with the sludge-containing solu' tion pumped from thetank 4 the sludge-containing solution may be pumped to two or morecleaners 14 and thence either directly or via a further centrifugalcleaner to one or more clarifiers 16 as illustrated in FIG. ,1.

The cleaner 14 is supported above the clarifier 16 and the latter ispreferably supported on an elevated platform, not shown, with a gangwaygiving access to the platform for the purpose of servicing of thecleaner 14 and the clarifier 16.

FIG. 4 illustrates a modified embodiment of FIG. 1 in whichconcentration of sludge is effected in two stages by two centrifugalcleaners 14 and 14a. Partly concentrated sludge is delivered through apipe 23a to the cleaner 14a and concentrated sludge is delivered fromthe cleaner 14a to the clarifier 16. Solution separated out in thecleaners 14, 14a is returned to the tank 4 by solution-retum pipes 26,26a.

H6. 5 illustrates an embodiment of the invention as applied to anexisting phosphating plant in which the tank 4 is provided withconcentrating cones 28. In such existing plant the cones 28 and pump 9are housed in a hole dug in the ground but when using the embodiment ofFIG. 1 it is not necessary to dig a hole to accommodate any of theplant.

In all embodiments of the apparatus the piping is preferably made ofstainless steel.

I claim:

1. Apparatus for pre-treating metal objects with a treating solution,for example with zinc-phosphate, comprising a tank to contain thesolution, spray nozzles arranged to apply solution to the objects, asolutionpump operable to pump solution from the tank to the spraynozzles through solution-delivery pipes connecting the solution pump tothe nozzles, a clarifier device operable to separate sludge fromsolution, a sludgedelivery pipe through which sludge and solution canpass from the bottom of the tank to the clarifier device, and asludge-pump operable continuously to transmit sludge and solution fromthe bottom of the tank through the sludge-delivery pipe to the clarifierdevice, wherein a sludge-concentrating device connected to thesludge-delivery pipe is operable to concentrate sludge to a flow ratethereof within the capacity of the clarifier device and the sludge-pumpis operable to transmit sludge and solution to the sludgeconcentratingdevice at a rate in excess of that of the capacity of the clarifierdevice to effect separation of sludge from solution.

2. Apparatus according to claim 1, wherein the sludge-concentratingdevice is a centrifugal cleaner.

3. Apparatus according to claim 1, wherein a solution-return pipeconnects the centrifugal cleaner to the tank to return to the tanksolution which has had its sludge content reduced by the centrifugalcleaner.

4. Apparatus according to claim 2, wherein the rate of flow of sludgefrom the centrifugal cleaner is controlled by an outlet opening ofpredetermined size.

5. Apparatus according to claim 2, wherein the rate of flow of sludgefrom the centrifugal cleaner is controlled by an adjustable valve.

6. Apparatus according to claim 1, wherein the sludge-pump is connecteddirectly to the bottom of the tank.

7. Apparatus according to claim 1, wherein the sludge-pump is connectedto the bottom of the tank through at least one sludge settling cone.

2. Apparatus according to claim 1, wherein the sludge-concentratingdevice is a centrifugal cleaner.
 3. Apparatus according to claim 1,wherein a solution-return pipe connects the centrifugal cleaner to thetank to return to the tank solution which has had its sludge contentreduced by the centrifugal cleaner.
 4. Apparatus according to claim 2,wherein the rate of flow of sludge from the centrifugal cleaner iscontrolled by an outlet opening of predetermined size.
 5. Apparatusaccording to claim 2, wherein the rate of flow of sludge from thecentrifugal cleaner is controlled by an adjustable valve.
 6. Apparatusaccording to claim 1, wherein the sludge-pump is connected directly tothe bottom of the tank.
 7. Apparatus according to claim 1, wherein thesludge-pump is connected to the bottom of the tank through at least onesludge settling cone.